Inclined kiln for the firing and sintering of material and a method for operating said kiln

ABSTRACT

An inclined kiln having an inclined run off surface bounded laterally by side walls, is provided with at least three burners for playing on different longitudinal zones of the runoff surface, the burners being controllable independently of each other for differential heating of the respective zones. Spent, burnt gases are drawn along the runoff surface and led from the upper end thereof to a recuperator in which the burnt gases give up heat for the pre-heating of atmospheric air for combustion of the burners.

[151 3,658,308 [451 Apr. 25, 1972 Y United States Patent Beckenbach [54] INCLINED KILN FOR THE FIRING AND SINTERING OF MATERIAL AND A METHOD FOR OPERATING SAID KILN Primary Examiner-John J. Cam

[72] Inventor: Karl Beckenbach, Hildegundisallu 33, Bu

derich, Dusseldorf, Germany Sept. 4, 1970 Attorney-Singer, Stern & Carlberg [22] Filed:

ABSTRACT combustion of the burners.

4 Claims, 5- Drawing Figures PATENTEDAPRZSIQTE 3.658308 In ventor" fiizr/ Bec/renZad z 14 orveeys The invention relates to a method of operating an inclined kiln for the firing and sintering of material, typically limestone, of the kind in which the material is fed from a feed shaft to the top end of an inclined laterally bounded runoff surface disposed inside a firing chamber, slides down the runoff surface while being played on by fuel gases produced by burners, and then leaves the firing chamber via an outlet disposed at the bottom end of the runoff surface. The invention also relates to the construction of an inclined kiln operated by such method.

In the prior art kilns of the kind referred to suited more particularly for the firing of limestone chips, the fuel gases playing on the material sliding down the runoff surfaces have been produced by two burners disposed one beside the other and jointly controlled, in which the fuel fed is burnt with preheated cooling air tapped from the cooling zone. There was hitherto been a failure to realize that the movement of the material sliding down over the lateral portions of the runoff surface is affected not only by the friction between such material and the runoff surface, but also by the friction between the material and the kiln side walls, so that such movement is delayed in comparison with the movement of the material sliding down in the central longitudinal zone of the runoff surface, between its lateral zones. The result of the difference between the speed at which the material runs down the lateral zones and the speed at which it runs down the central zone of the runoff surface, which usually widens to some extent towards its lower end is that at the lateral zones of the runoff surface, the material is played on by the fuel gases for a longer time than in the central zone so that the material is not uniformly fired.

I have also found that the uniformity of the rate at which the material slides down the runoff surface mainly depends on the extent to which the fuel gases penetrate and permeate the layer of material moving down the runoff surface, inadequate permeation of the material by the fuel gases also having a very adverse effect on the uniformity and quality of the end product.

It is therefore an object of the invention to obviate the aforementioned disadvantages and so improve the operation and design of an inclined kiln of the kind specified as to enable the resulting product to be fired with a higher degree of uniformity.

According to the invention the fuel gases are played differentially on the material sliding down in the longitudinal central zone of the runoff surface and the material sliding down at both sides of such central zone, and the waste gas used is drawn off from the furnace at a place or places disposed immediately above the top end of the runoff surface and is fed to a recuperator for preheating the combustion air.

The fact that the fuel gases play differentially on'the lateral and central zones of the runoff surface compensates for the different rates at which the material slides down in such zones, while the special manner in which the waste gases fed to the recuperator are drawn off forces such gases to penetrate the layer of material sliding downwards and partially to flow along the runoff surface, with the result that the rate at which the material slides down is further uniformized, and the material is more intensively heated, since it is more satisfactorily permeated by the fuel gases in this zone.

In contrast to the conventional arrangement of two superimposed burners, the kiln used for the performance of the method according to the invention has at least three burners, of which the or each central burner can be regulated separately from the lateral burners, the kiln according to the invention also having a recuperator which is connected to a waste gas removal line branched off at the top end of a runoff surface and heats the primary air fed to the burners.

An embodiment of a shaft kiln for the performance of the method according to the invention will now be described by way of example with reference to the diagrammatic drawings, wherein:

FIG. 1 is a diagrammatic longitudinal section through an inclined kiln having two superimposed firing chambers and a recuperator;

FIG. 2 is a crosssection, taken along the line 2-2 in FIG. 1;

FIG. 3 is a view of the top end of the runoff surface and the adjoining feed shaft wall, viewed in the direction of the arrows FIG. 4 is a partial longitudinal section showing a special embodiment of a burner port, and

FIG. 5 is a view of the burner port illustrated in FIG. 4 viewed in the direction of the arrows 5-5 in FIG. 4.

Referring to FIG. 1 an inclined kiln has two superimposed firing chambers 10,12. The top firing chamber 10 has a runoff surface 14 extending at an inclination downwardly from a feed shaft 16 to a transfer shaft 17 extending to the lower firing chamber 12.

The drawings do not show the charging devices disposed at the top end of the feed shaft. The runoff surface 18 of the lower firing chamber 12, which is of substantially the same dimensions as the upper firing chamber 10, but can alternatively be somewhat wider than the latter, is inclined oppositely to the runoff surface 14 of the upper firing chamber 10. An outlet cooling shaft 20 adjoins the lower firing chamber 12. The side walls 22-of the two firing chambers 10, 12 diverge slightly in the downward direction of the substantially perpendicular firing chamber, the walls 24 opposite the runoff surfaces 14, 18 widening to a corresponding extent.

Three burner ports 26 are disposed one beside the other at the top ends of each of the two end walls 24. Burners 28 are associated with the two lateral burner ports, a burner 30 being provided for the central firing chamber.

As can be seen from FIG. 2, the two lateral burners 28.play on the material sliding down at those lateral zones a of the runoff surfaces adjacent the firing chamber side walls 22, while the central burners 30 play on the central zone b of the runoff surfaces. The lateral burners 28 can be regulated separately from the central burners 30, thus enabling the fuel gases to play on the downwardly widening zones a with less intensity than on the central zone b.

Of course, a larger number than three burners can be provided, of which the central group of burners play on corresponding central zones of the runoff surfaces.

FIGS. 4 and 5 illustrate a special embodiment of a burner port 26a in which, unlike the ports 26, the two lateral wall portions 34 extend substantially perpendicularly, while the lower wall portion 36 is inclined downwardly. A port construction of this kind, which reduces the width of the ports associated with the individually regulatable burners in the horizontal direction, is more particularly suited for narrow firing chambers whose perpendicular end walls 24 are relatively narrow, so that three burner ports widening outwardly in all directions (i.e. as shown in FIG. 2) would be too close to each other.

Preferably the lower wall portion 36 is at an angle of more than 30 with the horizontal. Due to such inclination, the gases leaving the burner ports can play on a substantially larger portion of the layers of material sliding down the runoff surfaces 14, 18 than if the burner ports were constructed as shown in FIGS. 1 and 2. The larger inclination in comparison with the conventional burner port shapes (FIG. 1) also helps to prevent dust from collecting in the burner ports.

Unlike the prior art construction, the inclined kiln according to the invention has a recuperator 40 which preheats primary air fed to the burners directly from the surrounding atmosphere. Since the recuperator is of a construction which is well known in itself, eg of the form presently used for shaft kilns having perpendicular shafts, the recuperator is merely illustrated diagrammatically, the path for the waste gases being indicated by a chain-dot line and that for the intake air by a dotted line. The outlet end (indicated by the arrow associated with the dotted line) for the intake air is connected to the intake air feed line 41 of the burners, which are also supplied by fuel feed lines 4111. Maintenance of the burners is substantially simplified by the fact that clean air fed from the atmosphere is substituted for the primary air hitherto used, which was cooling air containing a lot of dust and drawn off from the top end of the cooling zone. However an even more important feature is that in accordance with the invention the waste gases fed to the recuperator are drawn off from the firing chamber through apertures 42 disposed adjacent the top end of the runoff surface and disposed one beside the other transversely thereof. The individual apertures 42 are connected via branch lines 43 to a line 45 extending to the recuperator. As can be seen from FIG. 2, preferably three apertures 42 are provided, associated with the respective zones a and b of the runoff surface. Associated with each of the three apertures, which have refractory linings, is a damper play 44 enabling gas flow through the apertures to be regulated individually. In the zone of the apertures 42 the top end of the runoff surface is somewhat lengthened upwards as against the feed shaft wall which intersects them.

This manner ofdrawing off the waste gases forces a substantial proportion of the fuel gases produced by the burners to penetrate the layer of material sliding downwards, and also partly play along the runoff surface, thus ensuring that the material is more satisfactorily permeated by the fuel gases and loosened up. so that the material is enabled to slide more satisfactorily and uniformly down the runoffsurface.

The waste gases flowing through the recuperator indirectly heat the intake air entering the recuperator to a temperature of 300400 C. The intake air is forced through the recuperator by a blower (not shown) and fed as primary air to the burners of the two firing chambers through air lines (not shown). A fan (not shown) is also provided for removing the waste gas by suction.

Preferably, waste gas is removed by suction through the drawing off apertures with which the top ends of the runoff surfaces of the top and bottom firing chambers are formed. The drawing-off apertures 42a of the lower firing chamber 12 (one of such apertures is shown in FIG. 1) are connected to the recuperator through a line shown diagrammatically by the chain line 45a. A damper 44a is associated with the aperture 42a.

The drawings do not show the conventional removal devices disposed at the bottom end of the outlet cooling shaft 20.

I claim:

1. A firing and sintering kiln, including a treatment chamber formed by two side walls, a first substantially vertical end wall, a second end wall, and a top wall, said second end wall having an interior surface inclined downwardly in the direction toward said first end wall to form between said first end wall and the lower edge of said inclined surface a discharge opening in said treatment chamber, said top wall having a material supply opening adjacent the top edge of said inclined interior surface of said second end wall, a plurality of burners associated with separate apertures in said first end wall, fuel supply means for said burners, said bumers and wall apertures being so arranged as to direct burning gas streams toward two side zones and an intermediate zone of said inclined end wall surface, first control means for the burners directing burning gas streams toward said the side zones, second control means for the burners directing burning gas streams toward said intermediate zone, whereby the intensity of heat treatment of material sliding down along said intermediate zone is controllable independently of the intensity of heat treatment of material sliding down along said side zones, means defining outlet openings for exhaust gas adjacent the top edge of said inclined end wall surface, and heat exchanger means in communication with said exhaust outlet openings for preheating combustion air for said burners.

2. A firing and sintering kiln according to claim 1, in which said wall apertures associated with said burners have substantially vertical parallel side walls and a bottom wall inclined downwardly toward the interior of said treatment chamber.

3. A firing and sintering kiln according to claim 1, including control means associated with said exhaust outlet openings for varying the size of said openings and thereby controlling the amount of exhaustgas discharged therethrou h.

4. A firing and sintering kllll according to c aim 1, including a second treatment chamber having its top supply opening in communication with the bottom discharge opening of said firstmentioned treatment chamber, said second treatment chamber including side walls, end walls, an inclined end wall surface, a top wall, a bottom discharge opening, burners and associated wall apertures of similar arrangement to corresponding elements of said firstmentioned treatment chamber, and exhaust gas outlet openings adjacent the top edge of the inclined end wall surface in said second treatment chamber in communication with said heat exchanger means. 

1. A firing and sintering kiln, including a treatment chamber formed by two side walls, a first substantially vertical end wall, a second end wall, and a top wall, said second end wall having an interioR surface inclined downwardly in the direction toward said first end wall to form between said first end wall and the lower edge of said inclined surface a discharge opening in said treatment chamber, said top wall having a material supply opening adjacent the top edge of said inclined interior surface of said second end wall, a plurality of burners associated with separate apertures in said first end wall, fuel supply means for said burners, said burners and wall apertures being so arranged as to direct burning gas streams toward two side zones and an intermediate zone of said inclined end wall surface, first control means for the burners directing burning gas streams toward said the side zones, second control means for the burners directing burning gas streams toward said intermediate zone, whereby the intensity of heat treatment of material sliding down along said intermediate zone is controllable independently of the intensity of heat treatment of material sliding down along said side zones, means defining outlet openings for exhaust gas adjacent the top edge of said inclined end wall surface, and heat exchanger means in communication with said exhaust outlet openings for preheating combustion air for said burners.
 2. A firing and sintering kiln according to claim 1, in which said wall apertures associated with said burners have substantially vertical parallel side walls and a bottom wall inclined downwardly toward the interior of said treatment chamber.
 3. A firing and sintering kiln according to claim 1, including control means associated with said exhaust outlet openings for varying the size of said openings and thereby controlling the amount of exhaust gas discharged therethrough.
 4. A firing and sintering kiln according to claim 1, including a second treatment chamber having its top supply opening in communication with the bottom discharge opening of said firstmentioned treatment chamber, said second treatment chamber including side walls, end walls, an inclined end wall surface, a top wall, a bottom discharge opening, burners and associated wall apertures of similar arrangement to corresponding elements of said firstmentioned treatment chamber, and exhaust gas outlet openings adjacent the top edge of the inclined end wall surface in said second treatment chamber in communication with said heat exchanger means. 